function, var, callback
in Programming on Javascript
Javascript Basic
Global var and Local var
That’s important !! need to understand diffrent of three examples.
// example 1
let TestValue = "Global";
function ChangeValue(){
let TestVaule = "Local";
}
document.write(TestValue);
// the answer is : Global
// example 2
let TestValue = "Global";
function ChangeValue(){
let TestVaule = "Local";
document.write(TestValue);
}
// the answer is : Local
// example 3
let TestValue = "Global";
function ChangeValue(){
TestVaule = "Local";
}
document.write(TestValue);
// the answer is : Local
Function as a value
Function is object in javascript. that means function can be value in javascript.
function a(){} // it means var a = function(){}
a = {
b:function(){ // b is methods of object a
}
}
// object a has key b and value function
function cal(func num){
return func(num)
}
function increase(num){
return num+1
}
function decrease(num){
return num-1
}
alert(cal(increase,1));
alert(cal(decrease,1));
Callback
function sortNumber(a,b){
return b-a;
}
var numbers = [20,10,9,8,7,6,5,4,3,2,1];
alert(numbers.sort(sortNumber)); // array [20,10,9,8,7,6,5,4,3,2,1]
// sortNumber is callback function.